1. Field of the Invention
This invention concerns a method for passive localization of a target, by a mobile surveillance system, for example an aircraft, carrying sensors. The invention applies in particular to the localization of targets whose signal transmission frequency is variable.
2. Description of the Related Art
The methods of passive localization of a target commonly used are based in particular on use of the Doppler effect. This type of method can only truly be used if the transmission frequency of the target is fixed. Otherwise, due to the variations in transmission frequency, it is impossible to determine the Doppler frequency easily.
On current aircraft the radar transmission systems with variable frequency are becoming more generalized and the use of methods based on determination of the Doppler frequency is therefore no longer efficient.
An objective of the invention is in particular to perform passive localization of a target whose transmission frequency is not necessarily fixed, but may be variable.
The invention therefore concerns a method for localization of a target by interferometric measurement on the signal received from the target. The signal transmitted by the target is acquired by detection means equipping a carrier. The method for localization of a target comprises at least two steps.
The first step is a measurement acquisition step which comprises at least two independent sequences for acquisition of the signal transmitted by the target. On each sequence the carrier follows a separate trajectory, with a non zero angle between the trajectories. These acquisition sequences are used to obtain independent measurement series.
The second step is a measurement processing step involving statistical processing. This processing is carried out on each measurement series to determine parameters characterizing the target, especially speed and distance parameters.
The particular advantage of the invention is that it can be used to estimate the target parameters, without the target having to transmit at fixed frequency.
The estimation of the target parameters offers the advantage of being carried out from a limited number of measurements.
Advantageously, use of a spherical coordinate system simplifies the expression of the theoretical model used, making it easier to estimate the target parameters.
The processing implemented by the method according to the invention is iterative. Advantageously, the target parameters can be accurately estimated by successive improvements.